In-cylinder Pressure Oscillations Research Articles

Characterizing the Multiscale Knock Energy of the in-Cylinder Pressure of Compound Combustion Engines Fueled with Dimethyl Ether.

A two-cylinder, direct injection, and four-stroke naturally aspirated diesel engine is reformed to the compound combustion engine fueled with dimethyl ether. The wavelet energy spectra of the in-cylinder pressure with normal combustion and knocking combustion in a compound combustion engine are experimentally studied. The effects of the port fuel quantity, engine load, and engine speed on them are analyzed. The multiscale knock energy characteristics of the in-cylinder pressure are investigated based on wavelet energy and the Shannon entropy-energy ratio. The result shows that the in-cylinder pressure oscillation tends to be violent with the increase of port fuel quantity, the peak in-cylinder pressure increases, and its crank angle phase advances. With the increase in port fuel quantity, the wavelet energy of high-frequency detail signals d1, d2, and d3 obtained from wavelet decomposition all increases and the Shannon entropy-energy ratio decreases. The high-frequency detail signal d1 is more sensitive than the other detail signals. The frequency band of 5-10 kHz is the knock characteristic frequency band. The energy of the detail signal d1 increases significantly during knocking combustion, and the oscillation range enlarges and moves forward. The wavelet energy of detail signal d1 is the largest, and the Shannon entropy-energy ratio is the smallest at different brake mean effective pressures and different engine speeds. The effect of brake mean effective pressure and engine speed on the values is not obvious, and the port fuel quantity is the main factor.

An unsupervised machine learning technique to identify knock from a knock signal time-frequency analysis

Knock is a characteristic phenomenon of spark ignition engines that can result in lower fuel efficiency and higher combustion temperatures. When it is not adequately identified and controlled, knock might lead to intensive engine damage. Knock detection methods are based on recognising the large in-cylinder pressure oscillations that resonate in the combustion chamber as a consequence of the rapid auto-ignition of the end-gas. However, in-cylinder pressure sensors may be invasive and expensive. In this work, a method for knock classification is proposed based on the knock sensor measurement, which is a low-cost and easy-to-implement vibration sensor. Unfortunately, the vibration of the engine block contains information from several phenomena, and only intensive knock can be identified by classical methods. To counteract the amount of noise, machine learning (ML) techniques are applied to the knock sensor signal. A training database composed of several operating conditions is used to extract the main characteristics of knock. The signal is analysed in the time-frequency domain by using the short-time Fourier transform (STFT), the features of the signal are obtained by singular value decomposition (SVD), and finally, support vector machine (SVM) techniques are used to identify outliers. Experimental data from a spark-ignited engine at 2000 rpm and 3000 rpm with spark advance steps was used to train and validate the method. Results are compared to state-of-the-art knock recognition methods based on pressure and knock sensors. The technique was able to detect 73% of the knock cycles, which was similar to the results achieved using the pressure sensor data (77%). Compared to another method using the knock sensor signal as well, the percentage of false negative cases was reduced by 20%.

Study on engineering application method of large-scale reaction mechanism in knock prediction

In this paper, a new engineering application method for gasoline engine knock prediction in a quasi-dimensional combustion model using a large-scale reaction mechanism is explored. First, an accelerated calculation strategy coupled with 1D calculation and large-scale reaction kinetics mechanism was developed to meet the needs of rapid automatic simulation in engineering. Secondly, a gasoline surrogate was created according to the test results of China 92# gasoline. The motor octane number (MON) and the research octane number (RON) values, which were closely related to knock, were calibrated using the detailed reaction mechanism. Then, the prediction of auto-ignition of unburned region was carried out combined with predicted burn rate model and cycle to cycle variation (CCV) model. The relationship between the experimental in-cylinder pressure oscillation and the simulated auto-ignition in the unburned region was established. The multi-conditions verification results of three engines with different displacement, compression ratio and combustion system arrangement show that the average errors of predicted knock CA50 are 1.6°CA, 1.8°CA and 1.9°CA respectively.

The effect of ignition intensity and in-cylinder pressure on the knock intensity and detonation formation in internal combustion engines

Engine downsizing with a higher compression ratio and a higher boosting pressure improves the thermal efficiency of engines. However, with further downsizing of engines, knock intensity is aggravated until super knock occurs which is accompanied by a detonation wave that potentially can destroy engines rapidly. Therefore, it is essential to reveal the parameters that influence the knock intensity and the formation of a super knock. Self-designed detonation bomb experiments and corresponding numerical simulations were conducted to explore the end-gas combustion mode as well as the knock intensity problem. The experiment was conducted at three typical in-cylinder pressures for representing different mixture energy densities, which classify the knock phenomenon into subcritical (lower pressure), critical (medium pressure) and supercritical (higher pressure) conditions. Spark ignitions with low and high intensity realized by adjusting the spark ignition energy were given in each condition, respectively. The in-cylinder combustion process and pressure oscillation process were monitored by the synchronous acquisition of three pressure sensors that were installed in different positions of the chamber. It is found that irrespective of the low or high ignition intensity, the super knock as well as the detonation would not occur at the lower pressure, and only mild knock occurs. At the medium pressure, the high ignition intensity would result in a detonation wave, while the low ignition intensity would not. At the higher pressure, despite the intensity of ignition, a detonation wave as well as the super knock would always occur. Therefore, the ignition intensity and the in-cylinder pressure are two essential factors that affect the knock intensity of engines.

Effect of pilot fuel properties on engine performance and combustion stability in a tri-fuel engine powered by premixed methane-hydrogen and diesel pilot

The present work investigates the effect of pilot fuel properties on TF combustion using premixed methane-hydrogen-air (CH4-H2-air) mixtures ignited by a small amount of diesel pilot. Especially, we are investigating the effect of the cetane number (CN) and aromatic content (AC) on TF combustion in a single-cylinder compression ignition (CI) engine at varying charge air temperatures (Tair = 25 °C, 40 °C, 55 °C) and H2 volume fractions (MH2 = 10%, 20%, 40% and 60%) at lean premixed charge mixture conditions (equivalence ratio φ = 0.5). The novelty and main findings of the work consist of the following features: 1) besides the effect of H2 concentration and charge-air temperature, pilot fuel properties also play a crucial role in TF combustion, even a small amount of diesel pilot could dramatically affect the engine performance and combustion stability, 2) the CN and AC are the key factors affect the ignition delay time (IDT) and indicated thermal efficiency (ITE), 3) the in-cylinder pressure oscillation analysis based on a novel Superlets (SL) approach indicates that pilot fuel properties are important to the combustion states and combustion stability.

Multiple spark plugs coupled with pressure sensors: A new approach for knock mechanism study on SI engines

Controlled knock combustion is the focus of academic and industrial research for modern spark-ignition engines to achieve higher thermal efficiency and better performance. To understand the knock formation mechanism, a refitted compression-ignition engine equipping with a port fuel injection system was operated under spark-ignition conditions. A customized liner with four side spark plugs was used to trigger controllable knock, through various spark strategies (e.g., spark number, timing, and location). Four side pressure sensors and a top sensor mounted on the cylinder head were used to record the knock pressure oscillation. Fast Fourier transform and wavelet analysis were performed to evaluate the frequency of pressure oscillations. The results showed that activating more spark plugs could promote knock propensity and intensity along with earlier CA50, but the knock was effectively suppressed when symmetrically activating four spark plugs simultaneously, indicating the fast flame propagation could suppress the knock occurrence. When triggering 2 or 3 spark plugs simultaneously, the in-cylinder pressure oscillations display very concentrated directionality among all the knocking cycles, indicating the distributing tendency of hot spots in these cases. With the activated spark plug number ranging from 1 to 3, the acoustic resonance focused on (1, 0) mode, while the four activated spark ignition led to higher (0, 1) mode, indicating the auto-ignition initiated close to the chamber center. Compared with the side sensors, the top sensor could recognize more resonance modes. Similar time ranges of frequency bands with fixed CA50 were noted for all spark plug numbers. Higher frequency signal decayed faster than lower during the knocking vibrations. As expected, we find that auto-ignition starts earlier when advancing the spark timing. Thereby more energy is released by knock, which explains the knock amplitude growth with earlier spark timing.

Investigation of the gas injection rate shape on combustion, knock and emissions behavior of a rotary engine with hydrogen direct-injection enrichment

The application of hydrogen direct-injection enrichment improves the performance of gasoline Wankel rotary engine, and the hydrogen injection strategy has a significant impact on combustion, knock, and emissions. The Z160F Wankel rotary engine was used as the investigated compact engine, and the simulation model was developed using CONVERGE software. The combustion, knock and emissions characteristics of the engine were studied with the different mass flow of hydrogen injection, i.e., the trapezoid, wedge, slope, triangle and rectangle type of gas injection rate shape. In the numerical simulations, the in-cylinder pressure oscillations were monitored using monitoring points, and the knock index (KI) was used as an evaluation indicator. The study revealed that the gas injection rate shape significantly affected the mixture of hydrogen and air, thus impacting combustion, knock and emissions. When the injection rate shape was rectangle, the flame speed was faster, the peak pressure in the cylinder was higher, and the corresponding crank angle was earlier, which led to higher pressure oscillations in the cylinder and larger KI. Based on the rectangle injection rate shape, the KI decreased by 75.81%, 33.47%, 26.46% and 76.58% for trapezoid, wedge, slope, and triangle, respectively, and the indicated mean effective pressure increased by 15.68%, 5.07%, 0.56% and 14.98%, respectively. Due to the small difference in maximum temperature, which resulted in very little variation in nitrogen oxides for each injection rate shape, the total hydrocarbon emissions of the trapezoid and triangle injection rate shape was high due to the delayed combustion phase. This paper provides a solution for direct hydrogen injection to improve the combustion, knock and emissions behavior of the rotary engine.

Safe operation of dual-fuel engines using constrained stochastic control

Premixed combustion strategies have the potential to achieve high thermal efficiency and to lower the engine-out emissions such as NOx. However, the combustion is initiated at several kernels which create high pressure gradients inside the cylinder. Similarly to knock in spark ignition engines, these gradients might be responsible of important pressure oscillations with a harmful potential for the engine. This work aims to analyze the in-cylinder pressure oscillations in a dual-fuel combustion engine and to determine the feedback variables, control actuators, and control approach for a safe engine operation. Three combustion modes were examined: fully, highly, and partially premixed, and three indexes were analyzed to characterize the safe operation of the engine: the maximum pressure rise rate, the ringing intensity, and the maximum amplitude of pressure oscillations (MAPO). Results show that operation constraints exclusively based on indicators such as the pressure rise rate are not sufficient for a proper limitation of the in-cylinder pressure oscillations. This paper explores the use of a knock-like controller for maintaining the resonance index magnitude under a predefined limit where the gasoline fraction and the main injection timing were selected as control variables. The proposed strategy shows the ability to maintain the percentage of cycles exceeding the specified limit at a desired threshold at each combustion mode in all the cylinders.

Parametric investigation of pre-injection on the combustion, knocking and emissions behaviour of a large marine four-stroke dual-fuel engine

This study aims at the parametric investigation of a large marine four-stroke dual-fuel engine in order to identify the pre-injection effects on the engine combustion, knocking and emissions parameters. A model was employed that was developed by integrating a 1-D engine model in AVL-BOOST and a 3-D CFD model in CONVERGE. The MAN 51/60DF marine engine is modelled and the simulation results were validated against experimental data. Subsequently, parametric runs for various pre-injection timings and mass ratios are performed and the simulation results are analysed and discussed. The derived in-cylinder pressure oscillations at determined points are employed to calculate the knock index (KI), which was used as an evaluation indicator for the knocking intensity. A number of pre-injection strategies with varying timing and fuel mass ratios are studied. This study results reveal that a lower knock trend and NOX emissions can be achieved by early pre-injection timing and increasing pre-injection fuel mass ratio. In addition, the medium pre-injection interval increases the engine IMEP while reducing the NOX and total hydrocarbon emissions. Larger pre-injection mass ratio reduce the KI and NOX emissions, but reduces IMEP and causes the wetted-wall phenomenon. Besides, the excessive pre-injection intervals and pre-injection mass ratio result in a change in combustion mode from the conventional diesel compression ignition mode to a two-stage auto-ignition mode. This study provides a better understanding of the underlying interactions of involved parameters and proposes pre-injection solutions to improve the engine performance, emissions and knocking behaviour.

Analysis of in-cylinder pressure oscillation and its effect on wall heat transfer

In-cylinder pressure oscillations in internal combustion engines have been associated with increased heat losses and damages to the engine components. The links between the acoustic waves and the increased heat transfer (and potentially ensuing engine damages) have not yet been well understood. In this study, a high-fidelity large eddy simulation model incorporating an auto-ignition model is used to simulate the combustion process and the associated pressure oscillation at various engine operating conditions. The study serves to develop a better understanding of the acoustic waves in a combustion chamber and their effect on wall heat transfer. First, a simplified model of the pressure oscillations is proposed and shown to accurately characterize the pressure in the combustion chamber. Second, the simplified pressure model and acoustic theory are leveraged to develop a model of the in-cylinder gas velocities. Finally, a heat transfer model is presented that takes into consideration the pressure/velocity oscillations and the inherent acoustic properties of the trapped gas. The increase in heat transfer is shown to primarily stem from an increased heat transfer coefficient due to the velocity oscillations of the trapped gas. The results are consistent with previously observed experimental measurements of the heat flux in the presence of pressure oscillations.

A real-time pressure wave model for knock prediction and control

This article develops a control-oriented real-time zero-dimensional knock pressure wave model for spark-ignited engines based on the reaction-based two-zone combustion model developed earlier. This knock pressure wave model is capable of predicting the in-cylinder pressure oscillations under knocking combustion in real-time and can be used for the model-based knock prediction and control. A pressure wave equation including the knock deadening behavior is proposed, simplified, and used to calculate the pressure perturbations generated by knock combustion. The boundary and initial conditions at knock onset are analyzed and the analytic solution of the pressure wave equation is obtained. The model is calibrated and validated over two engine operating conditions at knock limit. The chemical kinetic-based Arrhenius integral and the maximum amplitude of pressure oscillations are used as the evaluation methods for knock onset and intensity prediction, and the knock frequency is studied using a fast Fourier transform of the filtered in-cylinder pressure oscillations. The simulation results show that the proposed knock pressure wave model is able to predict the knock onset timing, frequency, and intensity accurately under two engine operating conditions. Furthermore, the knock characteristics associated with gas mixture properties at intake valve closing is analyzed based on the experimental data, and their effect to knock cycle-to-cycle variation is also studied for the proposed model.

Effects of equivalence ratio and pilot fuel mass on ignition/extinction and pressure oscillation in a methane/diesel engine with pre-chamber

For reducing emissions and saving energy, pilot-ignited methane/diesel engines are attracting considerable attention as an alternative to traditional diesel engines. However, this dual-fuel engine suffers from poor ignition characteristics and knock occurrence under specific operating conditions. Thus, the present study comprehensively aims to address the effect of the CH4 equivalence ratio and pilot fuel amount on the ignition/extinction process, in-cylinder pressure oscillation, and engine performance in a low-speed dual-fuel engine with pre-chamber. The results show that the fuel-mixture ignition delay is prolonged with a decrease in the CH4 equivalence ratio, but it decreases as the pilot fuel amount increases. However, beyond a certain amount, an additional increase in pilot fuel will not affect the methane combustion, indicated engine power, and emissions. It was also found that extinction occurs with a CH4 equivalence ratio of 0.3, because the reaction of the low-temperature intermediate species CH2O becomes almost stagnant. The increase in CH4 equivalence ratio can improve the engine power, but it also induces pressure oscillation and promotes nitrogen oxide production. Moreover, the pressure oscillation or maximum amplitude of pressure oscillation (MAPO) increases with the increase in pilot fuel amount, although it has no significant change when the pilot fuel proportion is beyond 1.5%. The present study can provide a theoretical basis for improving the combustion stability of dual-fuel engines under low engine load and avoiding the risk of knock under moderate to high engine loads.

Online Measuring Method for the Engines’ IVC Timing Based on the In-Cylinder Pressure Fluctuation

The in-cylinder pressure fluctuations caused by intake valve closure (IVC) event were first investigated experimentally based on a single cylinder diesel engine with different cams. The experimental results show that the occurrence of the in-cylinder pressure fluctuation during the compression stroke has a close correlation with the IVC event. The start time of the pressure oscillation advances as the IVC timing advances. With a fixed IVC timing, higher engine speed results in a larger fluctuation amplitude and a longer fluctuation duration. To explain these phenomena, a numerical simulation model has been adopted. Results show that the IVC event causes pressure oscillations in both the cylinder and intake runner. At the same engine speed, the amplitude of the pressure oscillation decreases first and then increases as the IVC retards due to the change of gas flow direction. With the same intake temperature, the absolute time delay keeps constant at different engine speeds and IVC timings. The absolute time delay decreases as the intake temperature decreases. Based on the conclusions above, the potential methods to use the pressure oscillation are also discussed. An innovative engine valve timing detection method on the basis of in-cylinder pressure oscillation is presented.

Flame Propagation and Combustion Phenomena in a Confined Space with the Perforated Plate at Different Positions

ABSTRACTFlame acceleration and flame–shock interactions are important physical phenomena in combustion science. The primary contribution of this work is to observe different combustion phenomena in the flame acceleration process and during flame–shock interactions in a confined space with a perforated plate. The effect of the perforated plate is to generate a rapidly accelerating flame. The experiment is conducted with an improved experimental apparatus with larger optical windows to observe the complete flame development process and the results are obtained using high-speed Schlieren photography. The complete process is observed clearly, including jet flame formation, turbulent propagation, and shock formation and propagation. Meanwhile, the obvious propagation of the turbulent flame, shock waves and reflected shock waves in burnt and unburnt materials is observed clearly in our experiment in terms of flame–shock interactions. The present results indicate that the perforated plate positions can change the flame propagation as well as the in-cylinder pressure oscillation, and affect the combustion intensity in the confined space significantly. For the middle distance between spark plug and perforated plate (position A), the flame tip velocity after perforated plate increases with increasing hole size. In contrast, the significantly different flame propagation behaviors can be obviously observed for the small distance between the spark plug and perforated plate (position B). The flame tip velocity decreases with increasing hole size initially after the flame passes through the perforated plate. Subsequently, a large hole size results in a turbulent eddy with a larger eddy structure, and consequently the turbulent flame acceleration behavior becomes more obvious for the hole size of 5 mm. Furthermore, a reflected shock wave with a sequence of compression waves with oscillating propagation in the confined space is observed experimentally. The present work could provide valuable insights into super-knocking combustion in gasoline engine, fire-safe fields in mining operations and buildings.

Investigation of the Mechanism of In-cylinder Pressure Oscillation in Auxiliary Chamber Type Supercharged Gas Engine

Investigation of the Mechanism of In-cylinder Pressure Oscillation in Auxiliary Chamber Type Supercharged Gas Engine

An analysis of the in-cylinder pressure resonance excitation in internal combustion engines

This paper analyses the in-cylinder pressure oscillations in internal combustion engines, which are initiated by combustion and resonate during the expansion stroke. A specific mathematical tool, which takes into account the resonant frequency theory, has been developed to determine the resonance intensity evolution from the in-cylinder pressure signal.Two engines, a conventional spark-ignited (SI) engin modified to perform homogeneous charge compression ignition (HCCI) combustion, and a conventional compression ignited (CI) engine, were used to analyse the resonance excitation in various combustion modes at different operating conditions.The new transformation has been used to characterize resonance in various combustion modes and a previous method developed by the authors to estimate the trapped mass was fed by such knowledge to improve its robustness and accuracy.

Characteristics and effect factors of pressure oscillation in multi-injection DI diesel engine at high-load conditions

The in-cylinder pressure oscillation during combustion process in multi-injection (MI) DI diesel engine is researched in this paper. The in-cylinder pressure testing is conducted under different operating conditions and different injection parameters. The high-frequency pressure oscillation signal and the oscillation energy are extracted from the in-cylinder pressure signal. The time-frequency characteristics of the pressure oscillation in each combustion stage are analyzed using AGST. The effects of engine speed, load and injection parameters on pressure oscillation are investigated. Results show that for DI diesel engine with pilot-main injection strategy, the amplitude of pressure oscillation in pilot injection combustion (PIC) is the maximum and the oscillation energy in PIC is pretty high. Moreover, the pilot injection also shows important influences on pressure oscillation in main injection combustion. Generally, high engine speed and high load lead to drastic pressure oscillation. However, the pressure oscillation decreases when the engine speed rises above 2200r/min due to the influence of injection parameters. Under the same engine speed and load, the main injection advance angle and the pilot injection interval time show great influences on the amplitude, oscillation energy and time-frequency characteristics of pressure oscillation in each combustion stage, while the pilot injection quantity has less effects on the pressure oscillation when it varies in a narrow range. Based on the conclusions above, the potential methods to reduce the pressure oscillation are also discussed.

Experimental study on combustion pressure oscillation of soybean bio diesel oil

Abstract: The principal objectives of this study were to examine in-cylinder combustion pressure oscillation characteristics of soybean biodiesel in time domain and time-frequency domain, and their influences on the control and operational parameters, such as injection timing, exhaust gas recirculation (EGR) ratio, engine load and engine speed. In this study, the combustion pressure oscillation characteristics of biodiesel engine for various injection timing, EGR ratio and engine speed were investigated. The corresponding relation of pressure characteristics in the time domain and frequency domain were obtained. The results showed that the pressure oscillation and peak pressure rise acceleration occurred mainly in the diffusion combustion, and the peak pressure rise rate located in the premixed combustion. The in-cylinder pressure level curve can be divided into three stages. The pressure levels of stage 1, stage 2 and stage 3 represent the peak in-cylinder pressure, the maximum amplitude of pressure rise rate and pressure rise acceleration, respectively. As the injection timing retards, the pressure levels of stage 1 and stage 3 decrease gradually. The pressure level curve of stage 3 with 25o before top dead center (BTDC) is the highest and the oscillation is the most significant. It is worth noting that the location of each stage with various operate conditions is not fixed. At 0.41 MPa indicated mean effective pressure (IMEP), with the increase of EGR rate, the pressure levels of stage 1 and stage 2 decrease gradually. The pressure level curve of stage 3 and the maximum amplitude of pressure rise acceleration with 0% EGR rate are the highest. The oscillation with 0% EGR rate is the most significant at 0.41 MPa IMEP. Compared to 0.41 MPa IMEP, the frequency bands of stage 1 and stage 2 at 1.1 MPa IMEP are relatively low due to the soft combustion in the cylinder. As EGR rate increases, the pressure level of stage 1 decreases, and those of stage 2 and stage 3 increase gradually. The oscillation with 30% EGR rate is the most significant. With the increase of engine speed, the pressure levels of stage 1 and stage 2 decrease, and move to the low frequency. The pressure level in the high frequency domain at 1600 r/min is less than that at 1100 r/min, and the combustion process is smooth. Keywords: combustion pressure oscillation, soybean biodiesel, injection timing, exhaust gas recirculation, engine speed DOI: 10.3965/j.ijabe.20160906.1680 Citation: Ma P, Liu H L, Liu S Y. Experimental study on combustion pressure oscillation of soybean bio diesel oil. Int J Agric & Biol Eng, 2016; 9(6): 156－166.

Experimental Investigation of the Impact of In-Cylinder Pressure Oscillations on Piston Heat Transfer

Experimental Investigation of the Impact of In-Cylinder Pressure Oscillations on Piston Heat Transfer

Experimental Study on In-Cylinder Pressure Oscillations of Homogenous Charge Compression Ignition–Direct Injection Combustion Engine Fueled With Dimethyl Ether

The in-cylinder pressure oscillations of a homogeneous charge compression ignition (HCCI)-DI engine fueled with dimethyl ether (DME) have been investigated using discrete wavelet transform (DWT) based on four different wavelet functions. The in-cylinder pressure is decomposed into three levels that contain three details D1, D2, and D3, and an approximation A1. In normal combustion, there are no obvious pressure impacts in three details due to smooth combustion process. The abnormal pressure oscillations occur in three details in knocking combustion, and the oscillation is most intense in D1. Its frequency band 5–10 kHz is the knock frequency band, and most high-frequency pressure oscillations and wavelet energy are in this frequency band. The pressure oscillations are located in the premixed combustion stage and diffusion combustion stage. Characteristics of in-cylinder pressure oscillations can be extracted using four wavelet functions “db4,” “db8,” “sym4,” and “sym8.” Extract abilities of four wavelet functions are different and wavelet db4 is suitable for pressure oscillation detection.